This invention concerns high ortho resole resins and varnishes and their process for manufacture. These resins are used broadly in laminated thermosetting products consisting essentially of fibrous sheet material such as cellulose paper, asbestos paper, cotton fabric or mat, asbestos fabric or mat, wood veneer, nylon fabric, glass fabric, etc., which are impregnated or coated with a thermosetting resin binder and consolidated under high temperature and pressure into hard products of high mechanical strength.
The principal resins used are phenolics made by the chemical combination and partial polymerization of formaldehyde and phenolic compounds, such as phenols, cresols or cresylic acid under carefully controlled conditions. These resins are dissolved in alcohol or alcohol-water or other suitable solvents to form varnish solutions with which the fibrous sheet materials may be impregnated or coated.
After impregnation and drying, the material is cut into sheets which are stacked together between metal plates and pressed under high temperatures and pressures to form laminated thermosetting sheets. During this operation the resin passes from a fusible soluble stage into one which is practically insoluble and infusible or thermoset.
The properties of laminated thermosetting materials can be varied over a large range by use of different sheet fillers, binder resins or laminating processes. The industry, however, has grouped these products into a reasonable number of grades or classes for most application.
On the basis of strength-weight ratios, laminated phenolics are among the strongest materials known. The high strength, excellent resistance to heat and moisture and good electrical properties account for its use in large volumes in all branches of the electrical and electronic industry having great commercial and consumer utility.
This dynamic industry has placed higher and higher performance and fabricating requirement on the phenolic resins used in laminated sheet materials. The resin suppliers and those skilled in the art are aware of these new requirements.
The phenolic resins principally used in laminated thermosetting industry have been prepared by the chemical combination and partial polymerization of formaldehyde and phenolic compounds and are of two classes known as "novolacs" and "resoles".
The novolac resins are phenolic resins in which the phenolic molecules are joined by methylene bridges located at the ortho-and para-positions relative to the phenolic hydroxyl groups with the polymer chain having phenolic end groups. Novolacs are usually prepared with acid catalysts using an excess of phenol over aldehyde. High ortho-novolacs are also known as prepared by a process disclosed in U.S. Pat. No. 3,476,707. The preferred process for preparation is with a catalyst system comprising an oxide or hydroxide of an electropositive metal and a halogen acid using an excess of phenol over aldehyde.
The "high-ortho" novolac resins are characterized by having mostly ortho/ortho methylene bridges. The novolac resins are thermoplastic and soluble in alcohols to form varnishes. As used in laminates they must be cured to insoluble, infusible resins with the addition of a source of formaldehyde, such as hexamethylenetetramine or paraform. The "high-ortho" resins are considered to have enhanced heat curing speeds over the conventional novolac resin.
Phenolic resole resins are prepared generally using an alkaline catalyst system with an excess of formaldehyde giving resins having high percentages of pendent methylol groups rather than phenolic end groups which give condensates with methylene groups. U.S. Pat. No. 3,485,797 discloses phenolic resole compositions produced by using a soluble divalent metal salt catalyst with an excess of aldehyde under substantially anhydrous conditions and in the presence of an inert organic diluent to produce a mixture of dimethyol compounds. These condensates analyzed as a mixture of 0,0'-dimethylol-phenol, 2,2'-dihydroxy 3,3'-dimethyolbenzylic ether and 2,2'-dihydroxy-3,3'-dimethyloldiphenylmethane. The preferred phenols disclosed in U.S. Pat. No. 3,485,797 are those that unsubstituted in the paraposition as well as the ortho-position for subsequent crosslinking reactions necessary for high reactivity. The most preferred are the unsubstituted phenol and the metasubstituted phenols being substituted either by a hydrocarbon radical, a oxyhydrocarbon radical or a halogen radical meta to the hydroxyl group.
Resole resin varnishes heretofore known when cured have generally suffered from a lack of properties for certain applications, for example, electrical properties, water resistance properties, and mechanical strength properties. Because of these deficiencies, there has been a long felt need in the art of resole resin varnishes for modified phenol-aldehyde resole resins which would overcome one or more of these deficiencies.
The novel "high ortho" resole resins of this invention have a much higher benzyl ether content than the typical resoles known to the art. A typical range of ether-linkage content would be 25-90% as contrasted with alkaline catalyzed which ranges 0-10%. The resulting methylene linkage content is lower averaging 10-75% as contrasted to the usual resole of at least 90%. Such resin varnishes form laminates with excellent water resistance, a high degree of post formability along with high bond strength and flexibility. The benzyl ether linkage has been found to be superior to the methylene linkage of the typical alkaline catalyzed resole in providing postformability and flexibility through the internal plasticization of the ether linkage as contrasted to the more rigid methylene linkage of the typical resole resin.
Other improved properties of the novel "high ortho" resoles that are associated with the higher benzyl ether structure are the ability of these novel resoles to:
(1) Impregnate paper and glass cloth more readily providing one-pass coatability because of lower viscosity. PA0 (2) Tolerate higher water contents in the paper and glass cloth during lamination. The more polar ether structure of the resole is more compatible and provides faster impregnation. PA0 (3) Provide greater compatibility with a wide range of polar and nonpolar plasticizers, flame retardants and other additives. PA0 (4) Provide greater stability in varnish storage than the usual methylene linked resoles. PA0 (A) from about 10 through 40 weight percent of compounds each molecule of which has: PA0 (B) from about 5 through 70 weight percent of compounds each molecule of which has: PA0 (C) from about 15 through 65 weight percent of compounds each molecule of which has: PA0 (D) from about 0 through 5 weight percent divinyl benzene, PA0 (E) provided that the sum total of all such compounds in any given such mixture of carbocyclic compounds is always 100 weight percent. PA0 (A) other inorganic halides, such as gallium, titanium, antimony and zinc halides (including ZnCl.sub.2); PA0 (B) inorganic acids such as sulphuric, phosphoric and the hydrogen halides (including HF); PA0 (c) activated clays, silica gel and alumina; PA0 (D) BF.sub.3 and BF.sub.3 organic complexes, such as complexes of BF.sub.3 with organic compounds, such as ethanol, butanol, glycol, phenol, cresol, anisole, ethyl ether, isopropyl ether, di-n-butyl ether, formic acid, acetic acid, propionic acid and the like, or with inorganic acids, such as phosphoric acid, sulfuric acid, and the like, and PA0 (E) alkyl, aryl and aralkyl sulfonic acids, such as ethanesulfonic acid, benzene sulfonic acid, benzene disulfonic acid, chlorobenzene sulfonic acid, 3,4-dichlorobenzene sulfonic acid, cresol sulfonic acids, phenol sulfonic acids, toluene sulfonic acids, xylene sulfonic acids, octylphenol sulfonic acid, .beta.-naphthalene sulfonic acid, 1-naphthol-4-sulfonic acid, and the like. PA0 (A) from about 30 to 75 weight percent of a dissolved mixture of a high ortho phenol-formaldehyde resole resin, PA0 (B) from about 0.5 to 15 weight percent of dissolved water, PA0 (C) the balance up to 100 weight percent of any given varnish being an organic liquid which:
This invention is directed particularly to varnishes of certain novel phenol-aldehyde resole resins in organic solvents. These varnishes are especially adapted for use in the manufacture of impregnated sheet materials and of laminates thereof. The products have high flexural strength, low water absorption and excellent electrical properties. These varnishes display lower viscosity and hence excellent penetration qualities as respects non-woven, sheet-like materials as compared to conventional resoles.